Various types of lamp - reflector combinations using discharge lamps rather than incandescent lamps are known. Discharge lamps have the advantage of high light output and long life. U.S. Pat. No. 3,721,850, Giller, describes a lamp in which a single-ended discharge lamp is used, located similar to an incandescent lamp.
It has then been proposed to utilize double-ended discharge lamps, that is, lamps having a pinch or press seal at both ends with an intermediate bulb-like extended discharge space. This provides for more reliable ignition of the lamp, particularly when it is still hot. Further, it provides for better insulation between the current supply leads, which are now separated from each other by the length of the lamp. Such a structure is shown, for example, in British Pat. No. 2,123,541 and in the referenced application U.S. Ser. No. 005,685, filed Jan. 21, 1987, Gaugel, now U.S. Pat. No. 4,722,039. The structure shown in the referenced application, assigned to the assignee of the present application, is particularly suitable.
Optimal utilization and distribution of the available light, and particularly if a shield is used to provide a depressed beam, can be obtained by locating the lamp axially with respect to the reflector, and to locate the lamp itself in a base which is passed through an opening in the reflector. The current supply lead to the lamp at the self-supported forward end--that is, the end remote from the apex of the reflector, and leading to the forward pinch seal, is carried along the side of the discharge vessel to the single base. The requisite spacing between the electrical terminals in the base can be selected to be much greater than in single-ended discharge lamps, since the spacing of the terminals within the base is independent of the size of the pinch or press seals of the lamp or light emitting element as such.
When a lamp having a self-supported forward end is used in automotive headlamps, it has been found that the vibrations and shocks to which the lamp is exposed in use in an automotive vehicle causes difficulty in maintenance of the light unit of the lamp within the reflector. The base typically of ceramic, may break due to material failure.